This invention relates to a speed control circuit for a series motor which is designed to employ a feed back using the method of full wave rectification and phase control.
Two thyristors are used for the full wave rectification and phase control (the method of full wave rectification and phase control using a triac is thus excluded), and a rectifying element is connected in series with a magnetic field coil to magnify the motor feed-back signal which is used in this method. The motor which is especially assembled in this apparatus, not only has to be produced specially for this purpose, but also careful attention must be paid to the wiring in order to avoid producing polarity at the terminals of the motor. Therefore, the problem has existed that the motor cannot be mass-produced and the unit cost of production becomes expensive because the motor cannot be exchanged for a conventional motor.
The object of this invention is to provide a speed control circuit for a series motor in which one thyristor is connected in series with the series motor and a trigger signal generating element is used in a gate signal generating circuit for said thyristor. A feed-back circuit which can adapt to a conventional motor is employed.